“Possible loss of precision” in my Java program

Question

I'm new to Java. I wrote the following code:

import java.io.*;
import java.lang.*;

public class distravel
{
    public static void main(String args[])
    {
        String a1,a2,a3;
        int x=2;
        float d,u,a,t;
         //d=distance travelled,u=initial velocity,a=acceleration,t=timeinterval

        try
        {
            InputStreamReader read=new InputStreamReader(System.in);
            BufferedReader buff=new BufferedReader(read);

            System.out.print("Enter the INTIAL VELOCITY:");
            a1=buff.readLine();
            u=Float.parseFloat(a1);
            System.out.print("Enter the ACCELERATION:");
            a2=buff.readLine();
            a=Float.parseFloat(a2);
            System.out.print("Enter the TIME:");
            a3=buff.readLine();
            t=Float.parseFloat(a3);

            d=((u*t)+a*Math.pow(t,x))/2F;

            System.out.print("The total DISTANCE TRAVELLED:"+d);
        }
        catch(Exception e)
        {}
    }
}

I get this error:

distravel.java28:possible loss of precision
                                   found           :double
                                   required        :float
                                   d=((u*t)+a*Math.pow(t,x))/2F;
                                                            ^

How can I resolve this?

Answer 1

d=((u*t)+a*Math.pow(t,x))/2F;

should be

d=(float)((u*t)+a*Math.pow(t,x))/2F;

or declare d as double as GrahamS suggested.

Answer 2

Don't use floats in your floating point math calculations unless you have a specific reason for doing so (you don't). The overhead for the preferred type, double, is not much higher and the benefit in accuracy is great.

Answer 3

Math.pow returns double so you have to have double for 'd'. Or you could also cast 'd' to float.

Answer 4

It is because Math.pow() returns a double which you then do some calculations with. No matter what calculations you do the precision you will have to deal with is double. Therefore, you get the error message. Solutions:
1) make the floats double
2) cast the result to float: d=(float)((u*t)+a*Math.pow(t,x))/2F;

Answer 5

因为你将变量声明为float意味着它占用随机存取内存上的四个字节空间，它无法将所有数据存储在ram中，所以你必须将变量声明为double然后才能工作。